WAVE PARTICLE PARADOX

 

TOPIC: -                                                                WAVE-PARTICLE PARADOX

INSTRUCTIONAL MATERIALS: - Chart showing electron diffraction experiment.

REFERENCES BOOK: -

1.FARINDE O. E e tal, ESSENTIAL PHYSICS FOR SSS, Tonad Publishing Limited.

2.M. W. ANYAKOHA (2011), NEW SCHOOL PHYSICS FOR SENIOR SECONDARY SCHOOLS, Africana first publishers. (pg 488-490)

3.INTERNET               

PREVIOUS KNOWLEDGE: -The  Students have been taught x-ray

 OBJECTIVES: -  At the end of the lesson students should be able to: -

1.       Identify phenomena which are only satisfactorily explained by assuming that matter behaves like waves and particle.

2.       Explain the uncertainty principle in very general terms and give examples.

CONTENT: -

WAVE-PARTICLE PARADOX

Matter sometimes behaves as a wave and at other times as particles. There are therefore two theories of matter- the waves theory and the particles theory.

Wave Nature of Matter

Electron Diffraction

The wave nature of x-ray was established by x-ray diffraction experiments. In the same way the Davission and Germer experiment establish the nature of electrons.

In the Davission and Germer experiment, a beam of electrons emitted from a heated filament was made to impinge on a layer of a thin metal film or crystal at C. The electrons were diffracted and the diffraction rings were produce on a photographic plate place behind the thin metal film as shown.

If the voltage, v, on the anode was increased, the velocity ,v, of the electrons was increase. The rings were then seen to become narrower. Hence the wavelength, Ʌ, of the electron waves decreases with increasing electron velocity.

                The wavelength of a material object is given by

                                                Ʌ =   

Where mv is the momentum of the object and h is the planck’s constant. Later experiments showed that proton, neutron and other particles also have the wave properties of diffraction.

I. PARTICLE NATURE OF MATTER.

a. PHOTOELECTRIC EFFECT

In photoelectric effect, it was shown that when light falls on a metal surface, electrons are emitted from the surface. Similarly when x-ray is allowed to fall on the surface of a thin sheet of metal like gold, the x-ray  not only produces diffraction pattern but also acting like particles they may collide with the atoms of the metal and eject electrons as in phase.

b. THE COMPTON EFFECT

when a single x-ray photon collides with a free electron, the electron recoils  off as thought  it were perfect  elastic  sphere.                  This  is the Compton effect. In this effect, the scattered photon has a slightly lower frequency than the incident x-ray photon. In this phenomenon, matter inform of x-ray is shown to behave as a particle. The recoiling photon and electron are able to conserve energy and momentum.

II.WAVE -PARTICLE DUALITY

The wave-particle duality refers to the idea that light and matter (such as electrons) have both wave and particle properties i.e. light behave either as a wave or as a particle but not as both simultaneously.

As in matter,  so is it with light. Some observable phenomena in the nature of light such as reflection, refraction, diffraction, interference and polarization can be interpreted or explained by assuming that light (or matter) behaves like waves. But other observable phenomena such as emission and absorption of light, photoelectricity, radiation of energy from heated bodies, thermionic emission can only be understood by assuming the particle nature of matter.

 

 

 

THE UNCERTAINTY PRINCIPLE

Heisenberg Uncertainty Principle states that it is impossible to know accurately the  exact position and momentum of a particles simultaneously. The uncertainty in the momentum multiplied by the uncertainty in the position approximately equals the planck’s constant, h,

Measurement  can only be expressed as probabilities. Heisenberg shows that

      ȡx . ȡP > h     ; ȡx . ȡV > h       ; ȡE . ȡt > h

where x; t, p,  and E are the uncertainties in the position; time; momentum and energy measurement.

PRESENTA TION

Step I: The teacher revises the previous topic.

 Step II: The teacher explains the wave nature of matter.

Step III: The teacher explains the particle nature of matter.

StepI V: The students chorus the observable phenomena of nature of matter.

Step VI: The teacher explains the uncertainty principle .

EVALUATION:

The teacher evaluates the lessons by asking the following questions:

1.       Identify phenomena which are only satisfactorily explained by assuming that matter behaves like waves and particle.

2.       Explain the uncertainty principle in very general terms and give examples.

  ASSIGNMENT

What is the full meaning of MASER and LASER